Air conditioner

ABSTRACT

An air conditioner may be provided that includes a plurality of compressors compressing a refrigerant, a first heat exchanger for condensing the refrigerant compressed in the compressors, a first expansion valve for expanding the condensed refrigerant, a second expansion valve for expanding the refrigerant emerging from the first expansion valve, and a second heat exchanger for evaporating the refrigerant emerging from the second expansion valve. The refrigerant from the first expansion valve may be guided such that a portion of the refrigerant is introduced into one of the compressors after bypassing the second expansion valve and the second heat exchanger, and a remaining portion of the refrigerant may be introduced into another one of the compressors after passing through the second expansion valve and second heat exchanger.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Korean Patent Application No.10-2010-0110417, filed Nov. 8, 2010, the subject matter of which isincorporated herein by reference.

BACKGROUND

1. Field

Embodiments of the present invention may relate to an air conditionerhaving a plurality of compressors.

2. Background

An air conditioner is an appliance for cooling/heating a room orpurifying air in the room by using a refrigeration cycle for arefrigerant. The refrigeration cycle may include a compressor, acondenser, an expansion device, and an evaporator.

An air conditioner may include a plurality of compressors for oneoutdoor unit. One or more compressors may selectively operate inaccordance with a load. The plurality of compressors may include firstand second compressors connected in parallel via a refrigerant suctionline and a refrigerant discharge line.

At a low load, only one of the first compressor and the secondcompressor may operate. On the other hand, at a high load, the firstcompressor and the second compressor may operate simultaneously.

When the first and second compressors operate simultaneously, therefrigerant compressed in the first compressor and the refrigerantcompressed in the second compressor may sequentially pass through anindoor heat exchanger, an expansion device, and an outdoor heatexchanger, and are then distributed to the first and second compressors.The resultant refrigerant may be sucked into the first and secondcompressors in a low-temperature and low-pressure state.

In such an air conditioner, a high electric power consumption and alarge refrigerant circulation amount may be required because alow-temperature and low-pressure refrigerant is sucked into the firstand second compressors.

BRIEF DESCRIPTION OF THE DRAWINGS

Arrangements and embodiments may be described in detail with referenceto the following drawings in which like reference numerals refer to likeelements and wherein:

FIG. 1 is a diagram of a refrigeration cycle in an air conditioneraccording to an exemplary embodiment of the present invention;

FIG. 2 is a diagram of a refrigerant flow in a refrigeration cycle in anair conditioner in an embodiment (of FIG. 1) when a second compressoroperates alone;

FIG. 3 is a diagram of a refrigerant flow in a refrigeration cycle in anair conditioner (of FIG. 1) when a first compressor operates alone;

FIG. 4 is a diagram of a refrigerant flow in a refrigeration cycle in anair conditioner of (FIG. 1) when a first compressor and a secondcompressor operate simultaneously;

FIG. 5 is a P-h diagram according to operation modes of a plurality ofcompressors in an embodiment (of FIG. 1);

FIG. 6 is a diagram of a refrigeration cycle in an air conditioneraccording to an exemplary embodiment of the present invention;

FIG. 7 is a diagram of a refrigerant flow in a refrigeration cycle in anair conditioner in an embodiment (of FIG. 6) when a second compressoroperates alone;

FIG. 8 is a diagram of a refrigerant flow in a refrigeration cycle in anair conditioner in an embodiment of (FIG. 6) when a first compressoroperates alone;

FIG. 9 is a diagram of a refrigerant flow in a refrigeration cycle in anair conditioner in an embodiment of (FIG. 6) when a first compressor anda second compressor operate simultaneously; and

FIG. 10 is a P-h diagram according to operation modes of a plurality ofcompressors in an embodiment of (FIG. 6).

DETAILED DESCRIPTION

FIG. 1 is a diagram of a refrigeration cycle in an air conditioneraccording to an exemplary embodiment of the present invention. FIG. 2 isa diagram of a refrigerant flow in a refrigeration cycle in an airconditioner in an embodiment when a second compressor operates alone.FIG. 3 is a diagram of a refrigerant flow in a refrigeration cycle in anair conditioner in an embodiment when a first compressor operates alone.FIG. 4 is a diagram of a refrigerant flow in a refrigeration cycle in anair conditioner in an embodiment when a first compressor and a secondcompressor operate simultaneously. FIG. 5 is a P-h diagram according tooperation modes of a plurality of compressors in an embodiment. Otherembodiments and configurations may also be provided.

The air conditioner may include a plurality of compressors 2, 8 forcompressing a refrigerant, a first heat exchanger 10 for condensing therefrigerant that emerges from the compressors 2, 8, a first expansionvalve 40 for expanding the refrigerant condensed by the first heatexchanger 10, a second expansion valve 42 for expanding the refrigerantthat emerges from the first expansion valve 40, a second heat exchanger12 for evaporating the refrigerant that emerges from the secondexpansion valve 42, and a variable refrigerant line 46 for guiding therefrigerant that emerges from the first expansion valve 40 to passthough the second expansion valve 42 and the second heat exchanger 12,or to bypass the second expansion valve 42 and the second heat exchanger12.

The variable refrigerant line 46 may guide the refrigerant that emergesfrom the first expansion valve 40 such that a first portion of therefrigerant is introduced into one of the plurality of compressors, suchas the compressor 8 after bypassing the second expansion valve 42 andthe second heat exchanger 12, with a second portion (or remainingportion) of the refrigerant being introduced into another one of theplurality of compressors, such as the compressor 2, or the variablerefrigerant line 46 to guide the refrigerant that emerges from the firstexpansion valve 40 such that an entirety of the refrigerant that emergesfrom the first expansion valve 40 is distributed to the plurality ofcompressors (such as the compressors 2 and 8) after passing through thesecond expansion valve 42 and the second heat exchanger 12.

The variable refrigerant line 46 may also guide the refrigerant thatemerges from the first expansion valve 40 such that an entirety of therefrigerant is introduced into one of the plurality of compressors (suchas the compressor 8) after passing through the second expansion valve 42and the second heat exchanger 12, such that an entirety of therefrigerant is introduced into another one of the plurality ofcompressors (such as the compressor 2) after passing through the secondexpansion valve 42 and the second heat exchanger 12, or such that anentirety of the refrigerant is distributed to the plurality ofcompressors 2 and 8 after passing through the second expansion valve 42and the second heat exchanger 12.

The plurality of compressors 2 and 8 may include two or threecompressors. The following description may be provided in conjunctionwith an example in which the plurality of compressors include twocompressors, namely the first compressor 2, and the second compressor 8connected to the first compressor 2 in parallel via a refrigerantsuction line 4 and a refrigerant discharge line 6.

In accordance with operating conditions, such as a load, the first andsecond compressors 2 and 8 may operate simultaneously or only one of thefirst and second compressors 2 and 8 may operate.

The first and second compressors 2 and 8 may have a same displacement ormay have different displacements.

Where the first and second compressors 2 and 8 have differentdisplacements, only the compressor 8 having a smaller displacement mayoperate, only the compressor 2 having a greater displacement mayoperate, and/or the compressors 2 and 8 may simultaneously operate, inaccordance with a load. Thus, the first and second compressors 2 and 8may have different displacements.

The air conditioner may have a plurality of partial-load operation modesand a full-load operation mode to meet various operating conditionsincluding an ambient temperature and a desired room temperature, forexample.

The load of the air conditioner may include a first partial loadacceptable by operation of a smaller-displacement of one of the firstand second compressors 2 and 8 alone. The load of the air conditionermay also include a second partial load that can not be accepted byoperation of the smaller-displacement one of the first and secondcompressors 2 and 8, but may be acceptable by operation of agreater-displacement one of the first and second compressors 2 and 8alone. The load of the air conditioner may also include a full load thatis acceptable by simultaneous operations of the first and secondcompressors 2 and 8, but can not be accepted by operation of thegreater-displacement one of the first and second compressors 2 and 8alone.

When the load of the air conditioner is not greater than the firstpartial load, a first partial-load operation mode may be carried out inwhich the smaller-displacement one of the first and second compressors 2and 8 may operate alone (without the other one of the first and secondcompressors 2, 8). On the other hand, when the load of the airconditioner is greater than the first partial load, but is not greaterthan a second partial load, a second partial-load operation mode, inwhich the greater-displacement one of the first and second compressors 2and 8 may operate alone (without the other one of the first and secondcompressors 2, 8). Additionally, when the load of the air conditioner isgreater than the second partial load, a full-load operation mode may becarried out in which the first and second compressors 2 and 8 operatesimultaneously.

Since a portion of the refrigerant that emerges from the first expansionvalve 40 may be compressed in the second compressor 8 after bypassingthe second expansion valve 42 and the second heat exchanger 12, thesecond compressor 8 may have a smaller displacement than the firstcompressor 2. The following description may be provided in conjunctionwith an example in which the second compressor 8 has a smallerdisplacement than the first compressor 2.

The first partial-load operation mode is a second compressor operationmode in which the second compressor 8 operates alone (without the firstcompressor 2), and the refrigerant that emerges from the first expansionvalve 40 flows to the second compressor 8 after passing through thesecond expansion valve 42 and the second heat exchanger 12, as shown inFIG. 2.

The second partial-load operation mode is a first compressor operationmode in which the first compressor 2 operates alone (without the secondcompressor 8), and the refrigerant emerging from the first expansionvalve 40 flows to the first compressor 2 after passing through thesecond expansion valve 42 and the second heat exchanger 12, as shown inFIG. 3.

The full-load operation mode is a first and second compressorsimultaneous operation mode in which the first and second compressors 2and 8 operate simultaneously, and a first portion of the refrigerantthat emerges (or is output) from the first expansion valve 40 flows tothe second compressor 8 after bypassing the second expansion valve 42and the second heat exchanger 12, whereas a second portion (or remainingportion) of the refrigerant that emerges (or is output) from the firstexpansion valve 40 flows to the first compressor 2 after bypassing thesecond expansion valve 42 and the second heat exchanger 12, as shown inFIG. 4.

A cooling mode or a heating mode may be selectively performed when theair conditioner includes a cooling/heating switching valve 14. In thecooling mode, the cooling/heating switching valve 14 may guide therefrigerant compressed in at least one of the first and secondcompressors 2 and 8 to the second heat exchanger 12, and may guide therefrigerant that evaporated in the first heat exchanger 10 to thecompressor that is in operation. In the heating mode, thecooling/heating switching valve 14 may guide the refrigerant compressedin at least one of the first and second compressors 2 and 8 to the firstheat exchanger 10, and may guide the refrigerant evaporated in thesecond heat exchanger 12 to the compressor that is in operation.

The cooling/heating switching valve 14 may be connected to the first andsecond compressors 2 and 8 via the refrigerant suction line 4 and therefrigerant discharge line 6. The cooling/heating switching valve 14 mayalso be connected to the first heat exchanger 10 via a cooling/heatingswitching valve-first heat exchanger connecting line 16. Additionally,the cooling/heating switching valve 14 may be connected to the secondheat exchanger 12 via a cooling/heating switching valve-second heatexchanger connecting line 18.

The refrigerant suction line 4 may have a branching point 22 where therefrigerant that emerges from the cooling/heating switching valve 14 isdistributed to the first compressor 2 and the second compressor 8. Therefrigerant suction line 4 may include a common suction line 24connected to the cooling/heating switching valve 14 and the branchingpoint 22, and suction lines 26 and 28 that branches from the commonsuction line 24. The suction line 26 may be a first compressor-sidesuction line for guiding the refrigerant that flows through the commonsuction line 24 to the first compressor 2. The suction line 28 may be asecond compressor-side suction line for guiding the refrigerant thatflows through the common suction line 24 to the second compressor 8.

The refrigerant discharge line 6 may have a joining point 32 where therefrigerant that emerges from the first compressor 2 may join therefrigerant that emerges from the second compressor 8. The refrigerantdischarge line 6 may include a common discharge line 34 connected to thecooling/heating switching valve 14 and the joining point 32, anddischarge lines 36 and 38 that join (or connect) to the common dischargeline 34. The discharge line 36 may be a first compressor-side dischargeline for guiding the refrigerant compressed by the first compressor 2via the joining point 32 to the common discharge line 34. The dischargeline 38 may be a second compressor-side discharge line for guiding therefrigerant compressed in the second compressor 8 via the joining point32 to the common discharge line 34. A first discharge-side check valve37 may be provided at the first compressor-side discharge line 36, toprevent the refrigerant compressed in the second compressor 8 fromflowing to the first compressor 2. A second discharge-side check valve39 may be provided at the second compressor-side discharge line 38 toprevent the refrigerant compressed in the first compressor 2 fromflowing to the second compressor 8.

The first heat exchanger 10 may evaporate the refrigerant in the coolingmode, and may condense the refrigerant in the heating mode. The firstexpansion valve 40 may be provided between the first heat exchanger 10and the second heat exchanger 12. In the heating mode, the firstexpansion valve 40 may expand the refrigerant that flows toward a bypassdevice 50 after being condensed in the first heat exchanger 10. Thefirst expansion valve 40 may include an electronic expansion valve (EEV)or a linear expansion valve (LEV) in which an opening degree isadjustable. The bypass device 50 may be described below.

In the air conditioner, the first heat exchanger 10 may be provided inan indoor unit I, whereas the first compressor 2, the second compressor8, the second heat exchanger 12, the second expansion valve 42, thefirst expansion valve 40, and the variable refrigerant line 46 may beprovided in an outdoor unit O.

An indoor expansion valve 11 may be provided in the indoor unit I toexpand the refrigerant flowing to the first heat exchanger 10 in thecooling mode. The indoor expansion valve 11 may include an EEV or a LEVin which an opening degree is adjustable. In the cooling mode, theindoor expansion valve 11 may expand the refrigerant that passes throughthe second expansion valve 42 and the first expansion valve 40. In theheating mode, the indoor expansion valve 11 may be fully opened to allowthe refrigerant emerging (or output) from the first heat exchanger 10 topass therethrough.

The bypass device 50 may be provided in the variable refrigerant line46. In addition to the bypass device 50, the variable refrigerant line46 may include a one-way valve 60. The bypass device 50 may guide aportion of the refrigerant emerging (or output) from the first expansionvalve 40 in the heating mode to bypass the second expansion valve 42 andthe second heat exchanger 12, and thus flow to a point between thebranching point 22 of the refrigerant suction line 4 and the secondcompressor 8. The one-way valve 60 may prevent the refrigerant emergingfrom the bypass device 50 from flowing to the branching point 22 of therefrigerant suction line 4.

The bypass device 50 may be a gas injection device for injectingrefrigerant into the second compressor 8 under a condition that therefrigerant is in a liquid phase. The bypass device 50 may be connectedbetween the branching point 22 of the refrigerant suction line 4 and thesecond compressor 8. The bypass device 50 may allow the refrigerant tobe introduced into the second compressor 8 in the heating mode under acondition that the refrigerant has low-temperature and low-pressureliquid-phase. The bypass device 50 may allow the refrigerant to beintroduced into the second compressor 8 under a condition that therefrigerant has an intermediate pressure that is less than acondensation pressure of the first heat exchanger 10, but is greaterthan the evaporation pressure of the second heat exchanger 12.

The bypass device 50 may include an inner heat exchanger 53 having afirst passage 51 for guiding the refrigerant to flow between the secondexpansion valve 42 and the first expansion valve 40, and a secondpassage 52 through which a refrigerant flows while exchanging heat withthe refrigerant in the first passage 51. The bypass device 50 mayinclude a first bypass passage 54 that has a first end connected betweenthe first passage 51 (of the inner heat exchanger 53) and the secondexpansion valve 42, and a second end connected to the second passage 52(of the inner heat exchanger 53).

The bypass device 50 may also include a second bypass passage 55 havinga first end connected to the second passage 52, and a second endconnected to the suction line 28 of the second compressor 8.

The inner heat exchanger 53 may be provided between the first expansionvalve 40 and the second expansion valve 42 to allow the refrigerant thatemerges from the first expansion valve 40 to flow to the secondexpansion valve 42, and to allow the refrigerant that emerges from thesecond expansion valve 42 to flow to the first expansion valve 40.

The bypass device 50 may further include a third expansion valve 56provided at the first bypass passage 54. The third expansion valve 56may include an LEV or an EEV in which an opening degree is adjustable.The third expansion valve 56 may have a smaller capacity than the firstexpansion valve 40 and the second expansion valve 42. When a capacity ofthe third expansion valve 56 is greater than or equal to a capacity ofthe first expansion valve 40 and the second expansion valve 42, there isa high possibility of the refrigerant, which is in a liquid phase, frombeing introduced into the second compressor 8. In this example, it maybe difficult to finely adjust pressure and temperature of therefrigerant introduced into the first bypass passage 54. On the otherhand, when the capacity of the third expansion valve 56 is less than thefirst expansion valve 40 and the second expansion valve 42, apossibility of the refrigerant, which is in a liquid phase, may beminimized from being introduced into the second compressor 8. In thisexample, pressure and temperature of the refrigerant introduced into thefirst bypass passage 54 may be more finely adjusted. The third expansionvalve 56 may control the refrigerant introduced into the first bypasspassage 54 to have a pressure less than a condensation pressure of thefirst heat exchanger 10, but greater than an evaporation pressure of thesecond heat exchanger 12. The third expansion valve 56 may be closed inthe cooling mode, irrespective of the load of the air conditioner. In afull-load heating mode, the third expansion valve 56 may be opened to apredetermined opening degree in order to allow the refrigerant to beintroduced into the second compressor 8 after passing through the bypassdevice 50. On the other hand, in a partial-load heating mode, the thirdexpansion valve 56 may be closed to prevent the refrigerant from passingthrough the bypass device 50.

The one-way valve 60 may be provided between the branching point 22 ofthe refrigerant suction line 4 and a connecting point 58 of the bypassdevice 50 to the refrigerant suction line 4. The one-way valve 60 mayinclude a check valve that guides the refrigerant passing through thebranching point 22 of the refrigerant suction line 4 to flow to thesecond compressor 8, while preventing the refrigerant emerging from thebypass device 50 from flowing to the first compressor 2.

The air conditioner may diversely control the first compressor 2, thesecond compressor 8 and the third expansion valve 56, in accordance witha heating load.

When the air conditioner is in a heating mode, and the load thereof is afirst-partial load or a second-partial load, the air conditioner may becontrolled such that the second compressor 8 operates, the firstcompressor 2 is in a stopped state, and the third expansion valve 56 isclosed.

On the other hand, when the air conditioner is in a heating mode, andthe load thereof is the full load, the air conditioner may be controlledsuch that the first and second compressors 2 and 8 operate, and thethird expansion valve 56 is opened.

Each of the first and second compressors 2 and 8 may be a constant speedcompressor that compresses a refrigerant at constant speed. Each of thefirst and second compressors 2 and 8 may be a variable displacementcompressor such as a variable displacement inverter compressor.Alternatively, one of the first and second compressors 2 and 8 may be aconstant speed compressor, whereas the other one of the first and secondcompressors 2 and 8 may be a variable displacement compressor.

Where one of the first and second compressors 2 and 8 is a variabledisplacement compressor, and the other one of the first and secondcompressors 2 and 8 is a constant speed compressor, the air conditionermay more diversely cope with load.

Where the first compressor 2 is a variable displacement compressor, andthe second compressor 8 is a constant speed compressor, one of thesecond compressor operation mode or the first and second compressorsimultaneous operation mode may be selectively performed in accordancewith the first partial load or full load without performing one of thesecond compressor operation mode, first compressor operation mode, andfirst and second compressor simultaneous operation mode in accordancewith the first partial load, the second partial load, or the full load.

That is, at a partial load not greater than the first partial load, onlythe second compressor 8 may operate to cope with the partial load. At aload greater than the first partial load, but not greater than the fullload, the second compressor 8 may operate, and the first compressor 2may operate in a variable displacement mode to achieve load balancing.Accordingly, it may be possible to efficiently cope with a load greaterthan the first partial load as well as a load not greater than the firstpartial load, while minimizing an electric power consumption.

For example, where the first compressor 2 is a 5HP variable displacementcompressor, and the second compressor 8 is a 2HP constant speedcompressor, the second compressor 8 may operate alone at a partial loadcorresponding to 2HP or less (namely the second compressor operationmode). On the other hand, at a load corresponding to a displacementgreater than 2HP, but not greater than 7HP (for example, 3H, 4H, 5H, 6H,or 7H), the second compressor 8 may operate (for 2H), and the firstcompressor 2 may operate in a variable displacement mode to achieve loadbalancing (1H, 2H, 3H, 4H, or 5H) (i.e., the first and second compressorsimultaneous operation mode). In this example, the first and secondcompressors 2 and 8 may efficiently cope with a load up to 7H.

On the other hand, where the first compressor 2 is a constant speedcompressor, and the second compressor 8 is a variable displacementcompressor, one of the second compressor operation mode, the firstcompressor operation mode, and first and second compressor simultaneousoperation mode may be selectively performed in accordance with the firstpartial load, the second partial load, or the full load.

For example, where the first compressor 2 is a 5HP constant speedcompressor, and the second compressor 8 is a 2HP variable displacementcompressor, the second compressor 8 may operate alone at a partial loadcorresponding to 2HP or lower (i.e., the second compressor operationmode). At a partial load corresponding to a displacement greater than2HP, but not greater than 5HP, the first compressor 2 may operate alone,irrespective of the level of the load (i.e., the first compressoroperation mode). On the other hand, at a load corresponding to adisplacement greater than 5HP, but not greater than 7HP (e.g. 6H or 7H),the first compressor 2 may operate (for 5H), and the second compressor 8may operate in a variable displacement mode to achieve load balancing(1H or 2H) (i.e., the first and second compressor simultaneous operationmode). In this example, the first and second compressors 2 and 8 mayefficiently cope with a load of 0 to 2H and a load of 5 to 7H. Also, itmay be possible to cope with a load corresponding to a displacementgreater than 2HP, but not greater than 5HP.

Where the first compressor 2 is a variable displacement compressor, andthe second compressor 8 is a constant speed compressor, an entirety ofthe load it may be efficiently coped with through the second compressoroperation and the first and second compressor simultaneous operation.Accordingly, the first compressor 2 may be a variable displacementcompressor having a greater displacement than the second compressor 8,and the second compressor 8 may be a constant speed compressor having asmaller displacement than the first compressor 2.

A volume ratio between the first and second compressors 2 and 8 may varyby adjusting an operation frequency of the first compressor 2. Throughthe volume ratio variation, one may control an intermediate pressure atwhich an optimal efficiency is obtained in accordance with operatingconditions.

Where the first compressor 2 is a variable displacement compressorhaving a greater displacement than the second compressor 8, and thesecond compressor 8 is a constant speed compressor having a smallerdisplacement than the first compressor 2, a load acceptable by operationof the second compressor 8 alone (without the first compressor) may beset to the partial load, and a load acceptable by simultaneousoperations of the first and second compressors 2 and 8 may be set to thefull load. When the load of the air conditioner is a partial heatingload, the second compressor 8 may operate, the first compressor 2 may bein a stopped state, and the third expansion valve 56 may be closed. Onthe other hand, when the load is a full heating load, the first andsecond compressors 2 and 8 may operate, and the third expansion valve 56may be opened.

Functions of the air conditioner as described above may be described inmore detail.

When the air conditioner is in the heating mode and in the secondcompressor operation mode in which the second compressor 8 operatesalone (without the first compressor 2), as shown in FIG. 2 and “A” ofFIG. 5, the refrigerant that is compressed in the second compressor 8(a), may be condensed in the first heat exchanger 10 (b). Therefrigerant may then be expanded in at least one of the first expansionvalve 40 and the second expansion valve 42 while passing through thefirst expansion valve 40, the inner heat exchanger 53 and the secondexpansion valve 42 (c). Thereafter, the refrigerant may evaporate in thesecond heat exchanger 12 (d), and may then return to the secondcompressor 8 after passing through the one-way valve 60. The refrigerantmay heat the first exchanger 10 while circulating through the secondcompressor 8, the first heat exchanger 10, the first expansion valve 40,the second expansion valve 42, the second heat exchanger 12, the one-wayvalve 60, and the second compressor 8.

Since the second compressor 8 has a smaller displacement than the firstcompressor 2, the second compressor operation mode, in which the secondcompressor 8 operates alone, may exhibit a lower compression work, alower condensation pressure, and a higher evaporation pressure than thefirst compressor operation mode, in which the first compressor 2operates alone, as shown in “A” and “B” of FIG. 5.

On the other hand, when the air conditioner is in the heating mode andin the first compressor operation mode, in which the first compressor 2operates alone, as shown in FIG. 3 and “B” of FIG. 5, the refrigerantthat is compressed in the first compressor 2 (e), may be condensed inthe first heat exchanger 10 (f). The refrigerant may then expand in atleast one of the first expansion valve 40 and the second expansion valve42 while passing through the first expansion valve 40, the inner heatexchanger 53, and the second expansion valve 42 (g). Thereafter, therefrigerant may evaporate in the second heat exchanger 12 (h), and maythen return to the first compressor 2. The refrigerant may heat thefirst exchanger 10 while circulating the first compressor 2, the firstheat exchanger 10, the first expansion valve 40, the second expansionvalve 42, and the second heat exchanger 12.

When the air conditioner is in the heating mode and in the first- andsecond-compressor simultaneous operation mode in which the first andsecond compressors 2 and 8 operate simultaneously, as shown in FIG. 4and “C” and “D” of FIG. 5, the refrigerant that is compressed in thefirst compressor 2 (i) may be joined with the refrigerant that iscompressed in the second compressor 8 (j). The joined refrigerant iscondensed in the first heat exchanger 10 (k) and is then passed throughthe first expansion valve 40.

A portion of the refrigerant passing through the first expansion valve40 flows to the first bypass passage 54, and then flows to the secondbypass passage 55 after being expanded by the third expansion valve 56(i), and passing through the second passage 52 of the inner heatexchanger 53 (m). The refrigerant flowing to the second bypass passage55 is sucked into the second compressor 8 without being sucked into thefirst compressor 2 in accordance with a function of the one-way valve60. The refrigerant is compressed in the second compressor 8 (j).

The remaining portion of the refrigerant passing through the firstexpansion valve 40, namely, the refrigerant that does not flow to thefirst bypass passage 54, may exchange heat with the refrigerant thatpasses through the second passage 52 (of the inner heat exchanger 53),while passing through the first passage 51 (of the inner heat exchanger53). Thereafter, this refrigerant is expanded by the second expansionvalve (n) and is then evaporated in the second heat exchanger 12 (o).The evaporated refrigerant is sucked into the first compressor 2 and isthen compressed (i).

In this example, the refrigerant may heat the first heat exchanger 10while not only circulating the first compressor 2, the first heatexchanger 10, the first expansion valve 40, the inner heat exchanger 53,the second expansion valve 42, the second heat exchanger 12, and thefirst compressor 2 (“C” of FIG. 5), but also circulating the secondcompressor 8, the first heat exchanger 10, the first expansion valve 40,the third expansion valve 56, the inner heat exchanger 53, and thesecond compressor 8 (“D” of FIG. 5).

It may be possible to introduce, into the first compressor 2, therefrigerant sequentially passing through the first expansion valve 40,the inner heat exchanger 53, the second expansion valve 42, and thesecond heat exchanger 12, and to introduce, into the second compressor8, the refrigerant sequentially passing through the first expansionvalve 40, the third expansion valve 56, and the inner heat exchanger 53while simultaneously operating the first and second compressors 2 and 8.Additionally, electric power consumption may be reduced but also densityof the refrigerant may be increased, thereby increasing an amount of therefrigerant circulating the air conditioner and enhancing capacity ofthe refrigerant, as compared to an example in which an entirety of alow-temperature and low-pressure refrigerant is compressed by a singlecompressor, by controlling pressure of the refrigerant such thatpressure of the refrigerant introduced into the second compressor 8 isgreater than pressure of the refrigerant introduced into the firstcompressor 2.

FIG. 6 is a diagram of a refrigeration cycle in an air conditioneraccording to an exemplary embodiment of the present invention. FIG. 7 isa diagram of a refrigerant flow in a refrigeration cycle in an airconditioner in an embodiment when a second compressor operates alone.FIG. 8 is a diagram of a refrigerant flow in a refrigeration cycle in anair conditioner in an embodiment when a first compressor operates alone.FIG. 9 is a diagram of a refrigerant flow in a refrigeration cycle in anair conditioner in an embodiment when the first and second compressorsoperate simultaneously. FIG. 10 is a P-h diagram according to operationmodes of a plurality of compressors in an embodiment. Other embodimentsand configurations may also be provided.

As shown in FIGS. 6 to 9, in an air conditioner according to anembodiment, the bypass device 50 may include a gas/liquid separator 62provided between the first expansion valve 40 and the second expansionvalve 42. The bypass device 50 may include a gas/liquid separatorconnecting passage 64 having a first connected to the gas/liquidseparator 62, and a second end connected to the suction line 28, inorder to guide a gas-phase refrigerant emerging from the gas/liquidseparator 62 to the suction line 28 of the second compressor 8.Configurations and functions of an air conditioner according to anembodiment, except for the bypass device 50, may be identical or similarto those of previous embodiments. Accordingly, no further descriptionmay be provided of identical or similar configurations and functions.

The gas/liquid separator 62 may separate liquid phase refrigerant andgas phase refrigerant from the refrigerant expanded by the firstexpansion valve 40. The gas/liquid separator 62 may be connected to thefirst expansion valve 40 by a first expansion valve connecting line, andmay be connected to the second expansion valve 42 by a second expansionvalve connecting line.

The bypass device 50 may further include a third expansion valve 66provided at the gas/liquid separator connecting passage 64. The thirdexpansion valve 66 may adjust an amount of the refrigerant flowing fromthe gas/liquid separator 62 to the gas/liquid separator connectingpassage 64. The third expansion valve 66 may include an EEV or a LEV inwhich an opening degree is adjustable. The third expansion valve 66 maybe closed when the first compressor 2 operates alone (without the secondcompressor 8), or the second compressor 8 operates alone (without thefirst compressor 2), and may be opened only when the first and secondcompressors 2 and 8 operate simultaneously.

The third expansion valve 66 may have a smaller capacity than the firstexpansion valve 40 and the second expansion valve 42. When the capacityof the third expansion valve 66 is greater than or equal to the capacityof the first expansion valve 40 and the second expansion valve 42, theremay be a high possibility of liquid phase refrigerant being introducedinto the second compressor 8. In this example, it may be difficult tofinely adjust pressure and temperature of the gas phase refrigerant thatemerges from the gas/liquid separator 62. On the other hand, when thethird expansion valve 66 has a smaller capacity than the first expansionvalve 40 and the second expansion valve 42, the possibility of theliquid phase refrigerant being introduced into the second compressor 8may be minimized, and pressure and temperature of the gas phaserefrigerant flowing to the first bypass passage 54 may be more finelyadjusted.

When the air conditioner is in a heating mode and in a second compressoroperation mode, in which the second compressor 8 operates alone, asshown in FIG. 7 and “A” of FIG. 10, the refrigerant that is compressedin the second compressor 8 (a), may be condensed in the first heatexchanger 10 (b). The refrigerant may then expand in at least one of thefirst expansion valve 40 and the second expansion valve 42 while passingthrough the first expansion valve 40, the gas/liquid separator 62, andthe second expansion valve 42 (c). Thereafter, the refrigerant mayevaporate in the second heat exchanger 12 (d), and may then return tothe second compressor 8 after passing through the one-way valve 60. Therefrigerant may heat the first exchanger 10 while circulating the secondcompressor 8, the first heat exchanger 10, the first expansion valve 40,the gas/liquid separator 62, the second expansion valve 42, the secondheat exchanger 12, the one-way valve 60, and the second compressor 8.

Since the second compressor 8 has a smaller displacement than the firstcompressor 2, the second compressor operation mode, in which the secondcompressor 8 operates alone (without the first compressor 2), mayexhibit a lower compression work, a lower condensation pressure, and ahigher evaporation pressure than a first compressor operation mode, inwhich the first compressor 2 operates alone (without the secondcompressor 8), as shown in “A” and “B” of FIG. 10.

On the other hand, when the air conditioner is in the heating mode andin the first compressor operation mode, in which the first compressor 2operates alone (without the second compressor 8), as shown in FIG. 8 and“B” of FIG. 10, the refrigerant that is compressed in the firstcompressor 2 (e), may be condensed in the first heat exchanger 10 (f).The refrigerant may then expand in at least one of the first expansionvalve 40 and the second expansion valve 42 while passing through thefirst expansion valve 40, the gas/liquid separator 62, and the secondexpansion valve 42 (g). Thereafter, the refrigerant may evaporate in thesecond heat exchanger 12 (h), and may then return to the firstcompressor 2. The refrigerant may heat the first exchanger 10 whilecirculating the first compressor 2, the first heat exchanger 10, thefirst expansion valve 40, the gas/liquid separator 62, the secondexpansion valve 42, and the second heat exchanger 12.

When the air conditioner is in the heating mode and in the first- andsecond-compressor simultaneous operation mode, in which the first andsecond compressors 2 and 8 operate simultaneously, as shown in FIG. 9and “C” and “D” of FIG. 10, the refrigerant that is compressed in thefirst compressor 2 (p) may join with the refrigerant that is compressedin the second compressor 8 (q). The joined refrigerant may be condensedin the first heat exchanger 10 (r), and may then primarily expand whilepassing through the first expansion valve 40 (s). The refrigerantprimarily expanded by the first expansion valve 40 may be introducedinto the gas/liquid separator 62 which in turn separates the refrigerantinto a gas phase refrigerant and a liquid phase refrigerant (t). The gasphase refrigerant from the gas/liquid separator 62 passes through thethird expansion valve 66, and then flows to the suction line 28 of thesecond compressor 8. In the second compressor 8, the gas phaserefrigerant is compressed (q). The liquid phase refrigerant from thegas/liquid separator 62 is secondarily expanded by the second expansionvalve 42 (u), and is then evaporated in the second heat exchanger 12(v). The evaporated refrigerant is sucked into the first compressor 2,and is then compressed (p).

In this example, the refrigerant may heat the first heat exchanger 10while not only circulating the first compressor 2, the first heatexchanger 10, the first expansion valve 40, the gas/liquid separator 62,the second expansion valve 42, the second heat exchanger 12, and thefirst compressor 2 (“E” of FIG. 10), but also circulating the secondcompressor 8, the first heat exchanger 10, the first expansion valve 40,the gas/liquid separator 62, the third expansion valve 66, and thesecond compressor 8 (“F” of FIG. 10).

It may be possible to introduce, into the first compressor 2, therefrigerant sequentially passing through the first expansion valve 40,the gas/liquid separator 62, the second expansion valve 42, and thesecond heat exchanger 12, and to introduce into the second compressor 8,the refrigerant sequentially passing through the first expansion valve40, the gas/liquid separator 62, and the third expansion valve 56 whilesimultaneously operating the first and second compressors 2 and 8.Additionally, electric power consumption may be reduced, but alsodensity of the refrigerant may be increased, thereby increasing anamount of the refrigerant circulating the air conditioner and enhancingcapacity of the refrigerant, as compared to an example in which anentirety of a low-temperature and low-pressure refrigerant is compressedby a single compressor, by controlling pressure of the refrigerant suchthat pressure of the refrigerant introduced into the second compressor 8is greater than pressure of the refrigerant introduced into the firstcompressor 2.

Where the first compressor 2 is a variable displacement compressorhaving a greater displacement than the second compressor 8, and thesecond compressor 8 is a constant speed compressor having a smallerdisplacement than the first compressor 2, as in a previous embodiment, aload acceptable by operation of the second compressor 8 alone may be setto a partial load, and a load acceptable by simultaneous operations ofthe first and second compressors 2 and 8 may be set to a full load. Whenthe load of the air conditioner is a partial heating load, the secondcompressor 8 may operate, the first compressor 2 may be in a stoppedstate, and the third expansion valve 56 may be closed. On the otherhand, when the load is a full heating load, the first and secondcompressors 2 and 8 may operate, and the third expansion valve 56 may beopened.

The air conditioner according to embodiment(s) may have advantages.

An amount of electric power consumed in all compressors of the airconditioner in a heating mode may be minimized, as compared to anexample in which an entirety of a low-temperature and low-pressurerefrigerant is compressed by a single compressor, because therefrigerant compressed in the first compressor and the refrigerantcompressed in the second compressor are sent to the first heat exchangerafter being mixed, and a gas portion of the refrigerant primarilyexpanded by the first expansion valve is compressed in the secondcompressor after bypassing the second expansion valve and the secondheat exchanger, whereas a liquid portion of the refrigerant primarilyexpanded by the first expansion valve is compressed in the firstcompressor after passing through the second expansion valve and thesecond heat exchanger.

Additionally, for a small heating load, the second compressor mayoperate alone to cope with the small heating load, whereas for a largeheating load, the first and second compressors may operatesimultaneously to cope with the large heating load.

A density of the refrigerant may be increased, and satisfy a requiredrefrigerant capacity by the second compressor, which has a smallerdisplacement than the first compressor, as compared to an example inwhich the refrigerant is compressed in the second compressor under acondition that the refrigerant has a lower pressure than the refrigerantin a primarily expanded state, because only a gas portion of theprimarily-expanded refrigerant is compressed in the second compressor.

Embodiments of the present invention may have been made in view of theabove problems, and may provide an air conditioner capable of optimallycoping with a heating load, reducing electric power consumption, andachieving an increase in heating capacity.

An air conditioner may include a first compressor, a second compressorconnected to the first compressor in parallel by a refrigerant suctionline and a refrigerant discharge line, a first heat exchanger forevaporating a refrigerant in a cooling mode, and condensing therefrigerant in a heating mode, a second heat exchanger for condensingthe refrigerant in the cooling mode, and evaporating the refrigerant inthe heating mode, a first expansion valve arranged between the firstheat exchanger and the second heat exchanger, a second expansion valvearranged between the first expansion valve and the second heatexchanger, a bypass device connected between a branching point of therefrigerant suction line and the second compressor, to guide a portionof the refrigerant that emerges from the first expansion valve, to flowto a point between the branching point of the refrigerant suction lineand the second compressor after bypassing the second expansion valve andthe second heat exchanger, and a one-way valve arranged between thebranching point of the refrigerant suction line and a connecting pointof the bypass device to the refrigerant suction line to prevent therefrigerant that emerges from the bypass device from flowing to thebranching point of the refrigerant suction line.

The second compressor may have a smaller displacement than the firstcompressor.

The first compressor may be a variable displacement compressor, and thesecond compressor may be a constant speed compressor.

The air conditioner may have a second compressor operation mode in whichthe second compressor operates alone, and the refrigerant that emergesfrom the first expansion valve may flow to the second compressor afterpassing through the second expansion valve and the second heatexchanger. The air conditioner may also have a first and secondcompressor simultaneous operation mode in which the first compressor andthe second compressor operate simultaneously, and a portion of therefrigerant that emerges from the first expansion valve to flow to thesecond compressor after bypassing the second expansion valve and thesecond heat exchanger, whereas a remaining portion of the refrigerantthat emerges from the first expansion valve to flow to the firstcompressor after passing through the second expansion valve and thesecond heat exchanger.

The air conditioner may selectively perform the second compressoroperation mode and the first and second compressor simultaneousoperation mode.

The air conditioner may further have a first compressor operation modein which the first compressor operates alone, and the refrigerant thatemerges from the first expansion valve flows to the first compressorafter passing through the second expansion valve and the second heatexchanger.

The air conditioner may selectively perform the second compressoroperation mode, the first and second compressor simultaneous operationmode, and the first compressor operation mode.

The bypass device may include an inner heat exchanger having a firstpassage for guiding the refrigerant to flow between the first expansionvalve and the second expansion valve, and a second passage through whichthe refrigerant passes while exchanging heat with the refrigerant thatpasses through the first passage, a first bypass passage having an endconnected between the first passage of the inner heat exchanger and thefirst expansion valve, and an opposite end connected to the secondpassage, and a second bypass passage having an end connected to thesecond passage, and an opposite end connected to a suction line of thesecond compressor.

The bypass device may further include a third expansion valve arrangedin the first bypass passage.

The third expansion valve may have a smaller capacity than the firstexpansion valve and the second expansion valve.

At a partial heating load, the second compressor may operate, the firstcompressor may be in a stopped state, and the third expansion valve maybe closed. At a full heating load, the first compressor and the secondcompressor may operate, and the third expansion valve may be opened.

The bypass device may include a gas/liquid separator arranged betweenthe first expansion valve and the second expansion valve, and agas/liquid separator connecting passage having an end connected to thegas/liquid separator, and an opposite end connected to a suction line ofthe second compressor to guide a gas portion of the refrigerant from thegas/liquid separator to flow to the suction line of the secondcompressor.

The bypass device may further include a third expansion valve arrangedin the gas/liquid separator connecting passage.

The third expansion valve may have a smaller capacity than the firstexpansion valve and the second expansion valve.

At a partial heating load, the second compressor may operate, the firstcompressor may be in a stopped state, and the third expansion valve maybe closed. At a full heating load, the first compressor and the secondcompressor may operate, and the third expansion valve may be opened.

An air conditioner may be provided that includes a plurality ofcompressors for compressing a refrigerant, a first heat exchanger forcondensing the refrigerant compressed in the compressors, a firstexpansion valve for expanding the refrigerant condensed in the firstheat exchanger, a second expansion valve for expanding the refrigerantemerging from the first expansion valve, and a second heat exchanger forevaporating the refrigerant emerging from the second expansion valve,wherein the refrigerant emerging from the first expansion valve isguided such that a portion of the refrigerant emerging from the firstexpansion valve is introduced into one of the plurality of compressorsafter bypassing the second expansion valve and the second heatexchanger, and a remaining portion of the refrigerant emerging from thefirst expansion valve is introduced into another one of the plurality ofcompressors after passing through the second expansion valve and thesecond heat exchanger, or such that the entirety of the refrigerantemerging from the first expansion valve is introduced into one of theplurality of compressors after passing through the second expansionvalve and the second heat exchanger.

The air conditioner may further include at least one of a gas/liquidseparator and an inner heat exchanger arranged between the firstexpansion valve and the second expansion valve, to guide only a gasportion of the refrigerant emerging from the first expansion valve to beintroduced into the one of the plurality of compressors.

The one of the plurality of compressors may be a constant speedcompressor, and the another one of the plurality of compressors may be avariable displacement compressor having a greater displacement than theconstant speed compressor.

An operation frequency of the variable displacement compressor may beadjusted to vary a volume ratio between the variable displacementcompressor and the constant speed compressor, thereby controlling anintermediate pressure at which an optimal efficiency is obtained inaccordance with operating conditions.

An air conditioner may be provided that includes a plurality ofcompressors for compressing a refrigerant, a first heat exchanger forcondensing the refrigerant compressed in the compressors, a firstexpansion valve for expanding the refrigerant condensed in the firstheat exchanger, a second expansion valve for expanding the refrigerantemerging from the first expansion valve, and a second heat exchanger forevaporating the refrigerant emerging from the second expansion valve.The refrigerant emerging from the first expansion valve is guided suchthat a portion of the refrigerant emerging from the first expansionvalve is introduced into one of the plurality of compressors afterbypassing the second expansion valve and the second heat exchanger, anda remaining portion of the refrigerant emerging from the first expansionvalve is introduced into another one of the plurality of compressorsafter passing through the second expansion valve and the second heatexchanger, or such that the entirety of the refrigerant emerging fromthe first expansion valve is introduced into at least one of theplurality of compressors after passing through the second expansionvalve and the second heat exchanger.

Any reference in this specification to “one embodiment,” “anembodiment,” “example embodiment,” etc., means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention. Theappearances of such phrases in various places in the specification arenot necessarily all referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with any embodiment, it is submitted that it is within thepurview of one skilled in the art to affect such feature, structure, orcharacteristic in connection with other ones of the embodiments.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis disclosure. More particularly, various variations and modificationsare possible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

1. An air conditioner comprising: a first compressor; a secondcompressor provided in parallel to the first compressor by a refrigerantsuction line and a refrigerant discharge line; a first heat exchanger toevaporate a refrigerant in a cooling mode, and to condense therefrigerant in a heating mode; a second heat exchanger to condense therefrigerant in the cooling mode, and to evaporate the refrigerant in theheating mode; a first expansion valve between the first heat exchangerand the second heat exchanger; a second expansion valve between thefirst expansion valve and the second heat exchanger; a bypass deviceconnected between a branching point of the refrigerant suction line andthe second compressor, to guide a portion of the refrigerant that isoutput from the first expansion valve to bypass the second expansionvalve and the second heat exchanger and to flow to a point between thebranching point of the refrigerant suction line and the secondcompressor; and a one-way valve between the branching point of therefrigerant suction line and a connecting point of the bypass device tothe refrigerant suction line, the one-way valve to prevent therefrigerant that is output from the bypass device from flowing to thebranching point of the refrigerant suction line.
 2. The air conditioneraccording to claim 1, wherein the second compressor has a smallerdisplacement than the first compressor.
 3. The air conditioner accordingto claim 2, wherein the first compressor is a variable displacementcompressor, and the second compressor is a constant speed compressor. 4.The air conditioner according to claim 1, wherein the air conditioneroperates in a first and second compressor simultaneous operation modeand operates in a second compressor operation mode, wherein the secondcompressor operation mode is a mode in which the second compressoroperates alone without the first compressor, and the refrigerant that isoutput from the first expansion valve flows to the second compressorafter passing through the second expansion valve and the second heatexchanger, and wherein the first and second compressor simultaneousoperation mode is a mode in which the first compressor and the secondcompressor operate simultaneously, and a first portion of therefrigerant that emerges from the first expansion valve bypass thesecond expansion valve and the second heat exchanger and flows to thesecond compressor, whereas a second portion of the refrigerant thatemerges from the first expansion valve passing through the secondexpansion valve and the second heat exchanger and flows to the firstcompressor.
 5. The air conditioner according to claim 4, wherein the airconditioner selectively performs the second compressor operation modeand the first and second compressor simultaneous operation mode.
 6. Theair conditioner according to claim 4, wherein the air conditionerfurther operates in a first compressor operation mode in which the firstcompressor operates alone without the second compressor, and therefrigerant that emerges from the first expansion valve passes throughthe second expansion valve and the second heat exchanger and flows tothe first compressor.
 7. The air conditioner according to claim 6,wherein the air conditioner selectively performs the second compressoroperation mode, the first and second compressor simultaneous operationmode, and the first compressor operation mode.
 8. The air conditioneraccording to claim 1, wherein the bypass device comprises: an inner heatexchanger having a first passage for guiding the refrigerant to flowbetween the first expansion valve and the second expansion valve, and asecond passage through which the refrigerant passes while exchangingheat with the refrigerant that passes through the first passage; a firstbypass passage having a first end connected between the first passage ofthe inner heat exchanger and the first expansion valve, and a second endconnected to the second passage of the inner heat exchanger; and asecond bypass passage having a first end connected to the secondpassage, and a second end connected to a suction line of the secondcompressor.
 9. The air conditioner according to claim 8, wherein thebypass device further comprises a third expansion valve provided at thefirst bypass passage.
 10. The air conditioner according to claim 9,wherein the third expansion valve has a smaller capacity than the firstexpansion valve and the second expansion valve.
 11. The air conditioneraccording to claim 9, wherein: at a partial heating load, the secondcompressor operates, the first compressor is in a stopped state, and thethird expansion valve is closed; and at a full heating load, the firstcompressor and the second compressor operate, and the third expansionvalve are opened.
 12. The air conditioner according to claim 1, whereinthe bypass device comprises: a gas/liquid separator provided between thefirst expansion valve and the second expansion valve; and a gas/liquidseparator connecting passage having a first end connected to thegas/liquid separator, and a second end connected to a suction line ofthe second compressor, and the gas/liquid separator to guide a gasportion of the refrigerant from the gas/liquid separator to flow to thesuction line of the second compressor.
 13. The air conditioner accordingto claim 12, wherein the bypass device further comprises a thirdexpansion valve provided at the gas/liquid separator connecting passage.14. The air conditioner according to claim 13, wherein the thirdexpansion valve has a smaller capacity than the first expansion valveand the second expansion valve.
 15. The air conditioner according toclaim 13, wherein: at a partial heating load, the second compressoroperates, the first compressor is in a stopped state, and the thirdexpansion valve is closed; and at a full heating load, the firstcompressor and the second compressor operate, and the third expansionvalve are opened.
 16. An air conditioner comprising: a plurality ofcompressors each to compress a refrigerant; a first heat exchanger tocondense the refrigerant compressed by at least one of the compressors;a first expansion valve to expand the refrigerant condensed by the firstheat exchanger; a second expansion valve to expand the refrigerant thatis output from the first expansion valve; and a second heat exchanger toevaporate the refrigerant that is output from the second expansionvalve, wherein a first portion of the refrigerant that is output fromthe first expansion valve is provided to a first one of the plurality ofcompressors after bypassing the second expansion valve and the secondheat exchanger, and a second portion of the refrigerant that is outputfrom the first expansion valve is provided to a second one of theplurality of compressors after passing through the second expansionvalve and the second heat exchanger, or an entirety of the refrigerantthat is output from the first expansion valve is provided to one of theplurality of compressors after passing through the second expansionvalve and the second heat exchanger.
 17. The air conditioner accordingto claim 16, further comprising a bypass device to guide the firstportion of the refrigerant and the second portion of the refrigerant.18. The air conditioner according to claim 17, wherein the bypass deviceincludes: a gas/liquid separator between the first expansion device andthe second expansion device; a gas/liquid separator connection passagehaving a first end connected to the gas/liquid separator and a secondend connected to a suction line of one of the compressors.
 19. The airconditioner according to claim 18, wherein the gas/liquid separatorreceives the refrigerant expanded by the first expansion valve andseparates liquid phase refrigerant and gas phase refrigerant.
 20. Theair conditioner according to claim 20, wherein the bypass device furtherincludes a third expansion device provided at the gas/liquid separatorconnecting passage to adjust an amount of the refrigerant flowingthrough the gas/liquid separator connecting passage.
 21. The airconditioner according to claim 20, wherein: at a partial heating load,the second one of compressor operates, the first compressor is in astopped state, and the third expansion valve is closed; and at a fullheating load, the first compressor and the second compressor operate,and the third expansion valve are opened.
 22. The air conditioneraccording to claim 16, further comprising: at least one of a gas/liquidseparator and an inner heat exchanger provided between the firstexpansion valve and the second expansion valve, to guide only a gasportion of the refrigerant that is output from the first expansion valveto the first one of the plurality of compressors.
 23. The airconditioner according to claim 16, wherein the first one of theplurality of compressors is a constant speed compressor, and the secondone of the plurality of compressors is a variable displacementcompressor having a greater displacement than the constant speedcompressor.
 24. The air conditioner according to claim 23, wherein anoperation frequency of the variable displacement compressor is adjustedto vary a volume ratio between the variable displacement compressor andthe constant speed compressor, an intermediate pressure is controlled atwhich an efficiency is obtained in accordance with operating conditions.